diff --git a/lib/mapValues.js b/lib/mapValues.js
index 240fc67c9..a0a947092 100644
--- a/lib/mapValues.js
+++ b/lib/mapValues.js
@@ -34,7 +34,9 @@ import doLimit from './internal/doLimit';
  *     f1: 'file1',
  *     f2: 'file2',
  *     f3: 'file3'
- * }, fs.stat, function(err, result) {
+ * }, function (file, key, callback) {
+ *   fs.stat(file, callback);
+ * }, function(err, result) {
  *     // results is now a map of stats for each file, e.g.
  *     // {
  *     //     f1: [stats for file1],